This invention relates to microwave devices, and, more particularly, to a design for a waveguide junction isolator that achieves relatively unvarying performance over a range of temperatures.
Microwaves (including millimeter waves) are high frequency waves in the gigahertz range that are widely used in communications and other applications due to their ability to carry a large amount of information. Microwaves can propagate either in a waveguide or through free space. The present invention relates to their propagation in a waveguide.
In a microwave waveguide system, there are sometimes junctions between several lengths of waveguide. In one type of commonly encountered junction, the Y-junction, three ports leading to separate waveguides lie in a plane and are oriented symmetrically from a central junction structure. In the absence of an isolator, microwaves entering the junction from one port propagate to the other two ports with diminished energy.
In many applications, however, it is desirable to be able to direct the microwave energy from one port entirely to another port, isolating the third port so that very little of the microwave energy flows to it. A microwave isolator is a known device that may be placed at the junction to perform the function of directing the microwave energy from one port to another port, while isolating a third port.
A microwave isolator of conventional design for use with a hollow microwave waveguide includes a ferrite cylinder within the waveguide walls at the center of the junction structure. Outside the waveguide walls on either side of the ferrite cylinder and aligned with its cylindrical axis are permanent magnets that produce a magnetic field through the ferrite cylinder. The design and operation of conventional microwave junction isolators are known in the art. The operation of the microwave junction isolator is determined by factors such as the wavelength of the microwave radiation, the physical size of the waveguide, the physical size of the ferrite cylinder and the magnet, the strength of the magnet, and the geometry of the isolator structure.
Microwave junction isolators must operate over a range of temperatures, both because the environment of the waveguide system may change and because the transmitted microwave energy heats the waveguides and other parts of the system. It is highly desirable that the isolator have properties that are relatively independent of temperature, and therefore various design modifications of the basic junction isolator have been developed with the objective of achieving a temperature-independent operation. These prior temperature-compensated designs have not been fully satisfactory, and do not achieve as temperature-independent an operation as desired.
There is therefore a need for an improved temperature-compensation approach for waveguide isolators. Such an approach should be operable with known types of waveguide junctions, and should achieve the isolation or circulation function with minimal temperature dependence of performance. The present invention fulfills this need, and further provides related advantages.